This invention relates to heating, ventilating and air conditioning (“HVAC”) systems that include at least two zones controlled by sensors, generally thermostats, located within the at least two zones that control corresponding dampers in ducts leading from usually a single HVAC source to the at least two zones.
In a conventional HAVC zoning system, conditioned air can be supplied to a plurality of zones, each zone being controlled by its own thermostat. Zoning systems for such an HVAC system typically includes zone dampers disposed in the ductwork for controlling the air flow of the conditioned air to the zones in response to the thermostat. These zoning systems control the flow of conditioned air to the plurality of zones independently so as to allow for independent control of the zone environments. As a result, at any given time a number of zone dampers may be open or closed. As the temperature in each zone is satisfied, its zone damper will close causing the static pressure in the duct system to rise. This rise in static duct pressure can result in an increase in noise and drafts due, in part, to an increase in air flow velocity though the ducts in zones still calling for conditioned air.
Conventionally, a bypass damper system is used to relieve excess static duct pressure. For example, a bypass damper can be connected between the supply and return air duct. If the bypass damper system determines that the air flow to a supply air duct is causing excess static duct pressure, then the bypass damper will be modulated open to recycle the conditioned air from the supply air duct to the return air duct. This implementation has the disadvantage of being energy inefficient, and hence an expensive way to solve the problem. Bypass dampers can also be expensive to install and difficult to setup. Elimination of the aforementioned bypass damper system could reduce the amount of HVAC system equipment, which, in turn, would reduce installation and maintenance costs.
What is needed is alternative apparatus that can effectively and efficiently control excess static duct pressure without resorting to the use of a bypass damper.